This is a revised proposal to extend ongoing studies on regulation of phenotypic expression in mononuclear phagocytes, a heterogeneous but important component of the immune system. The bone seeking isotope 89Sr, is used to create bone marrow (BM) deprived monocyte- depleted mice for the study of tissue macrophage functions. Such mice rapidly lose the capacity to express an immunosuppressive prostaglandin-secreting splenic Mphi (PGSM) induced by the immunomodulator, C. parvum. Eicosanoid metabolism in peritoneal Mphi, however, is unaffected by BM ablation. We wish to determine the origin of PGSM and the nature of regulatory influences of BM and spleen on Mphi eicosanoid metabolism. In addition, we wish to investigate another aspect of Mphi activation and the effects of enhanced IL-1 release on insulin release. Specific aim (SA) 1. To determine mechanisms regulating the expression of PGSM by C. parvum and other Mphi activators. Synthesis and release of eicosanoids by Mphi will be assessed by RIA, HPLC and TLC in relation to BM and spleen cell interactions in vivo and in vitro. Populations will be defined by differential radiosensitivity and selective shielding of BM and spleen. Contributions of cell-bound and soluble factors will be studied in vitro by incubating spleen and bone marrow cells from C. parvum primed and unprimed mice either mixed or separated by microporous filters. Restoration of PGSM in vivo will be studied by transfusions of BM from primed and unprimed donors into primed and unprimed syngeneic recipients. SA 2: To assess influences of microenvironmental factors on PGSM expression with in vivo grafts of primary BM stromal cells and the MC-1 stromal cell line in conjunction with in vitro co-cultures of stromal cells and splenic Mphi. SA 3: To determine the relationship of the Fcy1/y2b receptor, phospholipase A2 activity and Ca++ in flux to PGSM expression. Expression of this receptor correlates with PGSM activity following ip C. parvum in normal mice. SA 4: To determine whether Mphi metabolism altered by activation results in IL-modulation of insulin release. The project should provide useful information concerning environmental regulatory influences on Mphi function relating to metabolism, inflammation and non- specific aspects of immunologic activity.